Fresh look at lakes’ history

Controversial ... Lake Alexandrina consumes hundreds of gigalitres every year in evaporation.

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The historical salinity levels in the Murray River’s Lower Lakes have come into sharp focus with the public release of research by scientist Peter Gell.

While many people in northern Victoria may have visited the attractive region, particularly the historic town of Goolwa, they may well ask why we should be bothered with the science behind the lakes in another state, hundreds of kilometres away.

The answer is that the future of the lakes and the future of irrigation in Victoria and the southern Riverina have become tied together.

The Murray-Darling Basin is obliged to provide thousands of gigalitres of water every year to South Australia, with a large slab required to provide freshwater flows into the lakes, supporting the aquatic biota and bird life, and to provide enough flow to keep the Murray Mouth open.

The South Australians maintain that the huge lakes, Alexandrina and Albert, must be maintained as freshwater lakes; after all, the barrages were built to prevent seawater flowing up into the lakes after World War II.

But even the Wentworth Group of eminent scientists acknowledge there were other reasons for the construction of the barges:

‘‘In order to assist agriculture, maintain lake level heights for boats and provide for water for settlements bordering the Lower Lakes, five barrages were constructed on Lake Alexandrina just prior to World War II. The aim was to reduce the impact of saltwater incursions and thus keep freshwater levels stable,’’ the scientists told the South Australian Royal Commission into the Murray-Darling Basin Plan.

South Australia has plenty of reasons to want to keep the lakes fresh and maintain water levels; among them the water supply to lower Murray communities and the stability of water levels for the lifestyle properties being built on Hindmarsh Island.

This position might be praise-worthy purely from a South Australian perspective, but unfortunately the water required to fill the bill for keeping the lakes fresh is coming from productive agricultural use in northern Victoria and the Southern Riverina.

And the volumes are enormous.

The evaporation from the Lower Lakes alone runs somewhere between 700 and 800Gl, getting close to the average consumption by Goulburn-Murray Water’s irrigation consumers.

Professor Peter Gell’s new report reminds everyone involved in the debate over the Murray-Darling Basin that simply repeating the mantra that the lakes have to be fresh, does not necessarily mean this is how the lakes have always been.

Even the Wentworth Group acknowledges that prior to construction of the barrages on Lake Alexandrina in the late 1930s, there is historic evidence the Lower Lakes were periodically impacted by saltwater from the sea, particularly during drought episodes with low freshwater inflows to the lakes.

Again from the SA Royal Commission: ‘‘These episodes are part of the characteristic El Nino-La Nina cycle of droughts and flooding rains across south-east Australia.’’

Prof Gell’s report shows the science-based position is that the Lower Lakes were always a mostly estuarine system that only occasionally became predominantly fresh during large flood events.

‘‘This only changed to predominantly freshwater once the barrages were put in,’’ he said.

Prof Gell pointed out that South Australian agencies have cherry-picked research which suited the freshwater agenda, and ignored the primary source of the most reliable information.

‘‘In conclusion, the new interpretation and its widespread adoption have acted to obfuscate the original conclusions of several earlier, published palaeolimnological studies and have appeared to strongly influence the socio-political decision-making process that has laid down an outcome of great ecological, social and economic consequence for water management in Australia,’’ he said.